STRTOL(3) | Library Functions Manual | STRTOL(3)

# NAME

strtol, strtoll, strtoimax, strtoq — convert string value to a long, long long, intmax_t or quad_t integer

# LIBRARY

Standard C Library (libc, -lc)

# SYNOPSIS

#include <stdlib.h>
#include <limits.h>

long int
strtol(const char * restrict nptr, char ** restrict endptr, int base);

long long int
strtoll(const char * restrict nptr, char ** restrict endptr, int base);

#include <inttypes.h>

intmax_t
strtoimax(const char * restrict nptr, char ** restrict endptr, int base);

#include <sys/types.h>
#include <stdlib.h>
#include <limits.h>

quad_t
strtoq(const char * restrict nptr, char ** restrict endptr, int base);

# DESCRIPTION

The strtol() function converts the string in nptr to a long int value. The strtoll() function converts the string in nptr to a long long int value. The strtoimax() function converts the string in nptr to an intmax_t value. The strtoq() function converts the string in nptr to a quad_t value.

The conversion is done according to the given base, which must be between 2 and 36 inclusive, or be the special value 0.

The string may begin with an arbitrary amount of white space (as determined by isspace(3)) followed by a single optional ‘`+`’ or ‘`-`’ sign. If base is zero or 16, the string may then include a ‘`0x`’ prefix, and the number will be read in base 16; otherwise, a zero base is taken as 10 (decimal) unless the next character is ‘`0`’, in which case it is taken as 8 (octal).

The remainder of the string is converted to an appropriate value in the obvious manner, stopping at the first character which is not a valid digit in the given base. (In bases above 10, the letter ‘`A`’ in either upper or lower case represents 10, ‘`B`’ represents 11, and so forth, with ‘`Z`’ representing 35.)

If endptr is non-nil, the functions store the address of the first invalid character in *endptr. If there were no digits at all, however, the functions store the original value of nptr in *endptr. (Thus, if *nptr is not ‘`\0`’ but **endptr is ‘`\0`’ on return, the entire string was valid.)

# RETURN VALUES

The strtol() function returns the result of the conversion, unless the value would underflow or overflow. If an underflow occurs, strtol() returns LONG_MIN, strtoll() returns LLONG_MIN, and strtoimax() returns INTMAX_MIN. If an overflow occurs, strtol() returns LONG_MAX, strtoll() returns LLONG_MAX, and strtoimax() returns INTMAX_MAX. In these cases, errno is set to ERANGE. If the base argument is not supported then errno is set to EINVAL and the functions return 0.

If no error occurs, errno is left unchanged. This behavior (which is unlike most library functions) is guaranteed by the pertinent standards.

# EXAMPLES

Because the return value of strtol() cannot be used unambiguously to detect an error, errno is left unchanged after a successful call. To ensure that a string is a valid number (i.e., in range and containing no trailing characters), clear errno beforehand explicitly, then check it afterwards:

    char *ep;
    long lval;

    ...

    errno = 0;
    lval = strtol(buf, &ep, 10);
    if (ep == buf)
    	goto not_a_number;
    if (*ep != '\0')
    	goto trailing_garbage;
    if (errno) {
    	assert(errno == ERANGE);
    	assert(lval == LONG_MAX || lval == LONG_MIN);
    	goto out_of_range;
    }

This example will accept “12” but not “12foo” or “12\n”. If trailing whitespace is acceptable, further checks must be done on *ep; alternately, use sscanf(3).

If strtol() is being used instead of atoi(3), error checking is further complicated because the desired return value is an `int` rather than a `long`; however, on some architectures integers and long integers are the same size. Thus the following is necessary:

    char *ep;
    int ival;
    long lval;

    ...

    errno = 0;
    lval = strtol(buf, &ep, 10);
    if (ep == buf)
    	goto not_a_number;
    if (*ep != '\0')
    	goto trailing_garbage;
    if (errno == ERANGE || lval < INT_MIN || INT_MAX < lval)
    	goto out_of_range;
    assert(errno == 0);
    assert(INT_MIN <= lval);
    assert(lval <= INT_MAX);
    ival = lval;

# ERRORS

[EINVAL]
  The base is not between 2 and 36 and does not contain the special value 0.
[ERANGE]
  The given string was out of range; the value converted has been clamped.

# SEE ALSO

atof(3), atoi(3), atol(3), atoll(3), strtod(3), strtou(3), strtoul(3), strtoull(3), strtoumax(3)

# STANDARDS

The strtol() function conforms to ANSI X3.159-1989 (“ANSI C89”). The strtoll() and strtoimax() functions conform to ISO/IEC 9899:1999 (“ISO C99”).

The strtoq() function is a BSD legacy function equivalent to strtoll() and should not be used in a new code.

# BUGS

Ignores the current locale.

April 30, 2015 | NetBSD 7.2